Ankle joint for artificial limbs



p 1944- N. F. HARRINGTON ANKLE JOINT FOR ARTIFICIAL LIMBS Filed June 14, 1943 INVENTOR.

Patented Sept. 12, 1944 UNITED STATES PATENT OFFICE,

JOINT FOR ARTIFICIAL LIMBS .Noel F. Harrington, Los Angeles, Calif.

Application June 14, 1943, Serial No. 490,716

5 Claims.

My invention relates to artificial limbs and has particular reference to an ankle joint for use with an artificial leg and foot to reproduce both in shapeand action the effect of a normal ankle joint. 4

In the construction and operation of artificial legs considerable difficulty has been encountered in providing an ankle'joint which will provide both the universal pivot action of a normal ankle joint and at the same time provide for the absorption of shocks and to reproduce artificially a replica of muscular action of the normal muscles of the foot, ankle and leg in walking or other movements to be given to the artificial leg.

Previous types of ankle joints have consisted either of a single pivotal action in which the pivot extends transverse to the rest of the foot to provide a forward and rearward rocking motion between the leg and foot in a walking motion, while other types of legs have attempted to provide a limited amount of sidewise pivotal motion to aid in the adaptation of the foot to uneven surfaces upon which the foot maybe required to impinge or to rest, this latter motion being provided in an effort to avoid the twisting strains which would be placed upon the artificial leg where one or the other side of the foot would engage an upwardly extending projection such as a stone or uneven ground surface which would normally be encountered in a walking motion.

These previous devices, however, have not proved satisfactory largely for the reason that the pivotal joints are formed between metal parts which places substantial weights or masses at the end-of the leg, lending a considerable amount I of inertia to the pendulum action of the leg as it swings from front to back and making it difiicult for the wearer to control the movement of the leg and producing a noticeable lack of reality in the forward movement of the leg when walking.

Another defect in the previous constructions is that even though sidewise pivotal motion is given to the foot, the movement is not progressively retarded as would be accomplished by the natural muscular action of the normal ankle, with the result that the sidewise motion renders the leg and foot rather unstable and difiicult for the wearer to control.

It is, therefore, 'an object of my invention to provide an ankle joint for artificial legs in which a minimum of mass is provided in the ankle joint .150 thus reduce the moment of inertia in the pendulum action of the leg.

Another object of my invention is to provide .an ankle joint in which the joint between the leg and the foot is made through an elastic medium which will provide a universal pivotal action of the foot relative to the leg.

It is a still further object of my invention to provide an ankle joint of the character set forth in the preceding paragraph wherein the elastic medium is so arranged as to be readily yieldable in the initial pivotal movement but which will provide progressively increasing resistance to increase of the movement in a manner substantially duplicating the muscular action in a normal ankle joint.

Another object of my invention is to provide an ankle joint of the character described in which the leg and foot are connected near the rear of the foot by an elastic medium which will yield under compression at the instant of impact of the heel with the ground surface and then will provide an elastic tension between the leg and the heel as the leg pivots forward while the foot is still upon the ground, thus providing a replica oi the tension produced by normal ankle muscles as the normal leg and foot are rocked forwardly in the walking action.

Other objects and advantages of my invention will be apparent from a study of the following specifications, read in connection with the accompanying drawing, wherein:

Fig. 1 is an elevational view partly in section of an artificial leg and foot provided with the ankle joint of my invention;

Fig. 2 is a vertical sectional view of the leg, 'foot and joint illustrated in Fig. 1, asection'being taken along the line IIII of Fig. 1";

Fig. 3 is an elevational view partly in section of the leg, foot and jointshown in Fig. 11 and illustrating the position of the parts at the instant of impact of the heel with the ground surface in makinga walking step; and

Fig. 4 is 'an elevational View partly in section of the foot, leg and ankle in the next progressive portion of the walking movement.

Referring to the drawing, I have illustrated in 1 an artificial leg and foot comprising a leg member I which may be formed of any suitable material and of any desired shape, preferably hollow for the purpose of reducing the weight. The leg member I terminates .at its lower end in an end wall 2 to which is secured a metal plate 3 as by means of a stud 4 and a nut 5.

The foot member 6 may be constructed of any suitable material and given any desired shape so long as it is provided with a substantially fiat upper surface I to which may be secured a sec.- ond metal plate or foot plate 8 as by means of leg from front to back.

a stud 8 and a nut III, the under surface of the foot being preferably counterbored as indicated at II to provide a recess for the reception of the end of the stud 9 and the nut I8.

faces of the post I3 being preferably vulcanized to the surfaces of the plates 3' and 8, respectively, the post I3 preferably having a greater vertical dimension than the post I2 to provide for a greater amount of motion between the rear portion of the foot and leg than is permitted at foot and leg to yield relative to each other as the foot rocks forwardly upon the heel to place tension, and to aid in the provision for a substantially universal pivotal. action between the foot 6 and the leg I I prefer to form the post 'I2- about I a core I4 of rubber or similar material having fabric or similar reinforcing material included therein to render the core less yielding than the surrounding material of the post I2. The shape of the core I4 may be that of a sphere, though I prefer that it be circular in front to rear cross section and oval or elliptical in left to right cross section as is illustrated in Figs. 1 and 2. This shape provides for a short radius frontto rear pivoting action between thefoot and leg and provides also a; substantially long radius sidewise pivotal action to permit the foot to'be self-ad-r justing for uneven ground surfaces and thus reproducing the normal sidewise pivotal motion of a normal ankle joint.

With the construction of the post I2 and its the foot against the ground will be cushioned by the resiliency of the post I2, the post I2 tend- -ing to. compress by gradually and progressively core I4 as described, it will be apparent that during the normal walking motion the impacts of building up resistance to the compression as the downward pressure increases between the leg and foot, while at the same time the foot will yield sidewise to conform to lateral unevenness of the ground upon which the foot impinges with an ually increasing resistance to the yield as the downward pressure is exerted by the leg. I Thus both the cushioning effect of the normal ankle jointin the initial impact and the normalside- 'wise turning or yielding with its gradual'resistance to the yield of a normal ankle joint is effectively reproduced by my post I2.

The post I2 may be secured to the plates 3 and 8 in any suitable manner, though I prefer that the upper and lower surfaces of the post I2 be 1 vulcanized directly upon the plates 3 and 8, re-

spectively, so that no other interconnecting mechanism is needed. By using this vulcanized joint, the total Weight of the ankle joint may be kept at a minimum and the material of which action permitting ready initial yield and a grad-:

lected to provide a minimum of weight for these.

a minimum of weight.

Thus by dispensing with bolts and metal pivot joints, I am enabled to keep the mass at the ankle joint at a minimum and reduce the inertia effect in the pendulum action of the swinging of the Therear post I3 is likewise constructed of rubber cured to provide resiliency both incompresco the plates 3 and 8 are constructed may be se' 65 terconnection between the foot and leg but with plates 3 and 8.

sion and in tension, the upper and lower sun- .75

.the ball of the foot into contact with the ground surface. This action is a duplication of theaction of a normal ankle joint during this initial part of a walking step.

as the muscles of the normal ankle would lower the ball of the foot into contact with the groun surface,

Then as the leg portion swings forward above the now stationary portion of the foot the forces are reversed, the front post 1 2 having its forward section under compression, the core I 4 acting as the pivotal axis while the rear post I3 is placed in tension by the separation of the rear sections of the plate 3 and 8 from each other. Thus the rear post produces a .muscular-like action tending to lift the heel of the foot from the ground surface in substantially the same man- .ner as the normal muscular action of an ankle joint and the heel of the foot is resiliently raised from the ground surface after the leg 4 has pivotedto a natural forward position while the entire foot has been permitted to rest in contact with the ground surface.

In order to permit a relatively great amount of stretch in therear post I3 and yet insure the natural lifting of the heel, I prefer to providea reinforcing fabric strip I5 adjacent the rear of.

.the rear edges of the plates 3 and 8 and will insure the positive lifting of the heel when, ,inthe walking motion, the leg and'foot have assumed the positions shown substantially in Fig. 4.

While it will be understood that the front and .rear posts I2 maybe vmade'integral with each other, I prefer tor-form them as separate posts, providing a space I6 betweenthem, thus reducing the amount of material in the ankle joint and minimizing the mass or weight which will be concentrated at the joint.

To finish oil the joint and provide a smooth external appearance, the space between the extreme outer edges of the plates 8 and 3 may be filled with sponge rubber or other suitable yielding and preferably elastic material as indicated at I1 and I8 ecured to boththe upper and lower plates 3 and 8, respectively, as by suitable'adhesive or directly vulcanizing the material to the v From the foregoing it will be apparent that I have provided an ankle joint in which the weight concentrated at the ankle joint may be maintained at an extremely low value to thus provide for a more natural appearance in use and a greater ability of the wearer to control the swinging movements of the leg and foot.

It will also be noted that a natural pivotal action both front to rear and sidewise is provided in which the pivotal action is relatively free during the initial pivotal motion but is increasingly resisted as the pivotal motion i increased. At the same time both an adequate cushioning of impacts is provided as well as a strong tension action, tending to rock the foot upon the ball portion thereof as the leg pivots forward in a natural walking motion, the net result of which is to reproduce with great fidelity the action of a normal leg, foot and ankle joint.

While I have illustrated the posts l2 and I3 as being attached to metal plates which are in turn attached to the foot and leg portions, it will be apparent that the plates may be made of plastic or any other suitable composition having the necessary strength and rigidity and also that these posts may be attached in any suitable manner directly to the foot and leg portions, thus dispensing with the plates if desired.

It will also be apparent that by forming the posts and plate assemblies as a unit, the construction of the joints may be simplified, permitting the units to be maintained in stock and assembled on foot and leg portions as desired.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

I claim:

1. In an artificial leg, a leg member, a foot member, a post of resilient material interposed between the members to form a universal pivotal connection between said members, and a core of resilient material embedded in said post and having a resilience less than that of .said post for limiting the movement of said members toward less resilient material disposed between the upper and lower ends of said post for limiting the relative vertical movement of said members toward each other, and having a substantially circular cross section in a vertical plane extending lengthwise of said foot member and having an elliptical cross section in a vertical plane extending transversely of the length of said foot, whereby the outer surfaces of said core define the radii of the pivotal motion between the members.

3. In an artificial leg, a leg member, a foot member, a substantially non-resilient element disposed between said foot and leg members having curved upper and lower surfaces presented to said members to define a pivot about which said members may rock relative to each other, and elastic means interconnecting said members to resiliently limit the rocking movement permitted between said members.

4. In an artificial leg, a leg member, a foot member, a substantially non-resilient element disposed between said foot and leg members having curved upper and lower surfaces presented to said members to define a pivot about which said members may rock relative to each other, and. elastic means surrounding said non-resilient element and interconnecting said foot and leg members to resiliently limit the rocking movement of said foot and leg members relative to each other.

5. In an artificial leg, a leg member, a foot member, means interposed between said foot and leg members to space said members apart, said means being formed of resilient rubber material vulcanized to plates respectively secured to said foot and leg members, a core in said means of substantially non-resilient material disposed adjacent the forward portion of said foot and leg members to act as a fulcrum about which said members may have a limited universal pivotal movement, and a limiting strip embedded in said means toward the rear of said foot and leg members to limit the stretch of the rear portion of said means to a predetermined spacing of the rear portion of said foot and. leg members away from each other.

NOEL H RRI G ON. 

